The purpose of this project is to gain some understanding of the chemistry of the early events in hormone action. As many hormones do not enter their target cell, the plasma membrane is the site at which the hormone is bound and at which the cellular response is initiated. The response seems to be mediated in many cases by cyclic 3'5' adenosine monophosphate cyclic AMP which is formed as a result of hormonal stimulation of membrane-bound adenyl cyclase. We propose to purify and characterize adenylate cyclase from two sources: bovine brain and rat renal medulla. The enzyme from these sources have different physical properties and a comparison of their structure will yield insight into the organization of adenylate cyclase in different cells. The enzymes have been partially purified. Procedures are now being devised to purify it further on the quantities needed for precise chemical, physical and immunological studies.